It is known that in modern cooking ranges, for safety reasons, each burner of the cooking range is provided, usually next to the switching on electrode, with a thermocouple intended for controlling the safety solenoid valve of the gas tap coupled with the burner.
The thermocouples normally used for such task have an electrically conducting body fixed to the burner plate and which at a first end carries a tip provided with the so-called “hot junction” of the thermocouple, intended to remain in use immersed in the flame generated by the fire. A polarity wire and a ground or earth wire branch off the opposite end of the body, at the terminals of which an electro-motive force is generated in use, until the hot junction remains immersed in the flame, which keeps an electromagnet of the gas tap energized, allowing the gas supply to continue. If the flame goes off, the electromotive force stops and the electromagnet interrupts the gas supply.
The electromagnet that controls the gas supply forms an integrated assembly with the gas tap which, in most cases, is provided with a coaxial connector integrally obtained with the gas tap body; the coaxial connector has a male tip connector which is connected to a pole of the electromagnet, and a metal and conducting collar which surrounds the tip and which, through the same gas tap body, is connected to the other pole of the electromagnet.
According to EP0619460, the two thermocouple wires are connected to the electromagnet to supply it, through a coaxial connector complementary to that of the electromagnet/gas tap assembly and comprising a tubular head made of a non-conducting material wherein a female terminal is accommodated, connected to the polarity wire and adapted to couple with the male tip connector and around which a metal sleeve is supported with a radial clearance, connected to the ground wire and adapted to be interference fitted on the collar of the gas tap body that surrounds the tip.
An alternative solution is described in WO2004/088205, which teaches to connect the thermocouple wires with the coaxial connector provided on the electromagnet/gas tap assembly by means of a device comprising a tubular head of a non-conducting material which internally supports a female connector intended to couple with the tip and connected to the polarity wire and which laterally supports on the outside a slide made of conducting material and connected to the ground wire, which after the insertion of the female connector onto the tip can be made to slide transversally to the tip, through a side window of the head, until it snap fits straddling the collar.
The solutions described have some drawbacks. The connector of EP0619460 has a high insertion and disconnection force; moreover, it is very expensive as it must be made with relatively small tolerances, otherwise it would either be impossible to assemble or a poor electrical contact would be obtained which, even if it does not make the thermocouple work bad, increases the response time thereof due to the raising of the electrical resistance. The connector device of WO2004/088205 has a complex and expensive construction and, above all, has large overall dimensions when the slide protrudes laterally from the head. Moreover, the operator in charge of the assembly can insert the slide in operating position, inside the head, before inserting the female connector onto the tip; this improper use does not usually prevent the assembling by simple insertion of the head/female connector/slide assembly on the coaxial connector provided on the electromagnet/gas tap assembly but it usually causes the onset of a poor electric contact (with possible damage to the slide) which therefore extends the response times of the thermocouple. Finally, connectors of this type are not suitable for relatively frequent assembly/removal.
DE 19908496 does not overcome any of these drawbacks. In fact, the male coaxial connector is interference inserted into the female coaxial connector, the sleeve contact whereof is provided with notches and can therefore be “opened” to facilitate the insertion and reduce the insertion effort. On the other hand, the retaining force is low; for this reason, an annular ridge is provided on the female connector and an annular recess is provided on the male connector; in the insertion step, the annular ridge engages the recess allowing the sleeve contact to “close”; thereafter, a ring or retaining element is axially moved which surrounds the sleeve contact on the outside to prevent it from opening, thus keeping the ridge permanently engaged into the relative recess. If on the one side this solution reduces the insertion effort of the male connector into the female connector, it does not ensure a good electric contact and make the connector construction much more complex, since elements (annular ridge and recess) to be coupled need to be obtained. Moreover, the connector overall dimensions are greatly increased both in axial and in radial direction.